The invention relates to an improvement in a roll for machines used to produce or process paper-, cardboard-, textile-webs or the like, and particularly an improvement in certain prior art rolls discussed below. Rolls of this type, because of the specific use to which they are put, can be excited to unwanted vibrations. Vibration problems of this kind, arising in the press-sections and smoothing mechanisms of papermaking machines, have been described frequently in trade literature.
Examples:
1 DE-OS 33 06 838 (=U.S. Pat. No. 4,598,448) PA0 2. US-PS 3 512 475 PA0 3. DE-OS 31 51 001 (=U.S. Pat. No. 4,514,887) PA0 4. J. B. Wheeldon and Dr. R. W. Hoyland, The British Paper Board Industry Federation Spring Conference 11th to 12th of March 1981 "Practical Results of Vibration Analysis".
Claim 1 relates to an improvement of the roll known from Schiel et al. Claim 14 relates to an improvement of the roll of the roll known from Rauf et al. These unwanted vibrations are mainly contact-vibrations between two rolls. The roll according to the invention usually forms, with a counter-roll, a press-gap through which the web to be treated passes; it is preferably designed as a sag-compensating roll. However, the invention is also applicable to a single roll, e.g., a paper or felt guide-roll, which tends to vibrate in the range of its critical r.p.m.
Publication 1 describes a device for damping vibrations in a so-called floating roll. This is one of the many known designs of sag-adjusting rolls. The annular space between the stationary central axis and the rotating roll-shell is divided, by means of two longitudinal seals, into two semicircular chambers of approximately the same size, of the width of the machine, and filled with fluid. One of these chambers (that referred to in claim 1 as the "first chamber") is usually pressurized and serves to transfer a hydraulic supporting force from the central axis to the roll-shell. Fluid-cushions, isolated between the roll-shell and the central axis, are provided as the device for damping vibrations. Theoretical considerations indicate that the effect of this device is inadequate and it has not as yet had any practical application.
Another known sag-adjusting roll is described in publication 2 and also comprises a stationary central axis and a rotating roll-shell. In this case, two opposing sliding blocks are provided to transfer supporting forces from the central axis to the inner surface of the roll-shell, each of the said blocks being supported by a radially displaceable piston. Each of the pistons is guided in a recess 27 in the central axis. Both recesses may be acted upon from the outside by pressurized fluid; they may also be connected together by a certain number of choke-passages. One of these recesses therefore corresponds to the "first chamber" mentioned in claim 1, while the other corresponds to the "second chamber". This known arrangement is also intended to damp vibration of the roll-shell, but its effectiveness appears to be doubtful. In any case, the high cost of the two opposing shoes is unsatisfactory. This cost would be justified only if the roll, as provided for in Justus et al. were arranged between two counter-rolls and formed a press-gap with each of them. As a sag-adjusting roll for arrangements comprising a single press-gap, this known roll would not be suitable because substantially the same pressure would obtain in both "chambers" 27.
Publication 3 describes a sag-adjusting roll in which the transfer of supporting forces from the central axis to the roll-shell is effected with the aid of sliding blocks 8 which are radially mobile in relation to the central axis and comprise hydrostatic bearing pockets 18, 25. Located between sliding blocks 8 and the central axis are cylinder-spaces 14, 21 corresponding to the "first chamber" mentioned in claim 14. The cylinder spaces can be acted upon from the outside and are in communication, through so-called outlet-ducts 17, 24, with hydrostatic bearing pockets 18, 25. Here again, the purpose is to damp vibrations of the roll-shell. To this end, a resiliently acting and externally arranged pressure-accumulator 35 is connected to the pressure-medium line running to the pressure-areas, the said pressure-accumulator corresponding to the "second chamber" mentioned in claim 14. One disadvantage of this known device is that a relatively large volume of pressurized fluid must overflow continuously between the inner surface of the roll-shell and the edges of the bearing pockets. This fluid would leak out of the roll and would have to be replaced.